Various dyes including non-benzene series aromatic compounds are known. Typical examples include tropilium salt compound as illustrated in Japanese Patent Application (OPI) No. 91663/86 (the term "OPI" as used herein means a "published unexamined Japanese patent application") and azulene nucleus-containing dyes as illustrated in U.S. Pat. No. 4,565,761 and Japanese Patent Application (OPI) No. 27293/86.
Among non-benzene series aromatic compounds, cycloheptimidazole nucleus-containing compounds are illustrated in Japanese Patent Publication Nos. 14500/68, 12701/70 and 17273/70, U.S. Pat. No. 3,615,607, French Patent No. 1,492,418, Japanese Patent Publication No. 27706/74, Japanese Patent Application (OPI) Nos. 260516/85 and 125384/81, Japanese Patent Publication Nos. 48558/74, 20706/65, 20707/65, 20708/65 and 20709/65, etc.
However, methine dyes such as those containing a cycloheptimidazole nucleus has a substituent at the 1-position thereof and which is a 10.pi. electron series resonance terminal auxochrome have not been described up to the present.